The present invention relates to a film transfer apparatus which processes a sheet using a film.
Some types of film transfer apparatuses employ a cast curing technique called Cast & Cure or a technique called cold foiling. These techniques produce a good aesthetic effect on sheets. In the Cast & Cure technique, a film having undergone hologram embossing is cured while being in press contact with the surface of a sheet coated with a UV (ultraviolet) curing resin, thereby producing, for example, a hologram effect by casting. Also, in the cold foiling technique, a film having foil deposited on it is brought into press contact with the surface of a sheet having an adhesive printed on it, thereby transferring the foil onto the sheet. An improvement in performance of such a film transfer apparatus which produces a good aesthetic effect on a print product is actively in progress.
Japanese Patent Laid-Open No. 2008-296448 (patent literature 1), for example, proposes an apparatus capable of performing cold foiling (cold foil transfer) on a sheet and embossing while printing on the sheet.
Also, Japanese Patent Laid-Open No. 2006-315229 (patent literature 2) proposes an apparatus capable of printing on a sheet, and performing, for example, LC coating or hologram embossing called TRANS TUVC using the Cast & Cure technique of transferring the pattern of a film on a varnished surface.
In winding a film to finish an unwinding reel used in the film transfer apparatus, and further storing and transporting the unwinding reel in the physical distribution process, the unwinding reel may have a non-circular shape due to an eccentricity or deformation with respect to a perfect circle. Therefore, even when such an unwinding reel is set in an unwinder device (unwinding device) in the film transfer apparatus, and rotated at a speed corresponding to the sheet conveyance speed, the feed speed of the film unwound from the unwinding reel varies, so an error occurs as the film feed speed is not always equal to the sheet conveyance speed.
When a low-inertia unwinding reel is rotated at low speed to unreel a film, the error between the film feed speed and the sheet conveyance speed can be controlled small. However, if an unwinding reel has a larger diameter or width, its inertia has a considerable influence on the error, so rotation control by the unwinder device weakens due to a flywheel effect, thus making it difficult to reduce the error by this control. Furthermore, as the feed speed at which the unwinder device unreels a film rises, the performance limit of weak rotation control by the unwinder device has a more considerable influence on the error.
At the point of application (nip) of pressing upon transfer between a film transfer cylinder and impression cylinder in the film transfer apparatus, the film feed speed and sheet conveyance speed must be equal as the sheet and film are superposed on the impression cylinder. However, as described earlier, rotation control by the unwinder device is insufficient to make the film feed speed and the sheet conveyance speed exactly equal. For this reason, making the film feed speed and the sheet conveyance speed exactly equal requires a film storage device for temporarily storing a film unreeled from the unwinding reel, and supplying the film to the nip portion at the same speed as the sheet conveyance speed.
The film storage device practically uses a method of forming a U-shaped portion in a film inside and storing the film, thereby reducing and absorbing the difference between the length of the film unreeled from the unwinding reel and that of the film which passes through the nip portion. The U-shaped portion is formed by a flat portion serving as one side surface, a flat portion serving as the other side surface opposed to one side surface, and a semicircular, arcuated portion serving as the bottom surface between the two side surfaces. The U-shaped portion is formed so that one side surface, the bottom surface, and the other side surface are continuous with each other without bending of the bottom surface.
As a scheme of forming such a U-shaped portion, a scheme which uses a dancer roller disclosed in patent literature 1, or a scheme which uses an aerodynamic device disclosed in U.S. Pat. No. 6,230,616B1 (patent literature 3) is available.
The film used in the film transfer apparatus is a highly stretchable soft material formed using, as a base material, a high-polymer film having a very small thickness that falls within the range of 12 to 20 micrometers. The smaller the width of the film, the lower the tension to be applied to the film must become. When the film is unreeled from the unwinding reel at a higher speed, a fluctuation in tension inevitably occurs due to the above-mentioned factor. As the width of the film reduces, a fluctuation in tension must be absorbed so as to keep it smaller. However, in the scheme which uses a dancer roller, the force of inertia of the dancer roller has a considerable influence on the error, so a limit is imposed in combating this problem. Under the circumstances, the scheme which uses an aerodynamic device is becoming the current mainstream.
From the viewpoint of improving the productivity as well, it is desired to provide a high-speed sheet-fed offset rotary film transfer apparatus which can be equipped with an unwinding reel having a larger diameter and smaller width. When the film transfer apparatus is equipped with a large-diameter unwinding reel, a film length sufficient for film transfer can be ensured, thus saving the temporary stop time taken to refill a new unwinding reel. Also, when the film transfer apparatus is capable of a high-speed operation, film transfer can be completed in a shorter period of time than in the related art techniques.
Unfortunately, a set of upstream and downstream film transfer units sandwich a unit which performs a different type of processing. This makes it difficult to ensure a space to arrange a large-diameter unwinding reel, and an operation space for the arrangement.